1. Field of the Invention
The present invention relates to an image forming device, e.g. a copier, facsimile, printer, that includes a cleaning blade to sweep away toner left on an image carrier. More particularly, the present invention relates to a device which supplies lubricant to a contact portion between the cleaning blade and the image carrier in order to reduce friction between the cleaning blade and image carrier.
2. Discussion of the Background
An image forming apparatus, such as an electrostatic copying machine, printer, facsimile, etc., that employs an electrophotography process may include a cleaning device for sweeping away toner left on an image carrier. A conventional cleaning device includes a cleaning blade which contacts an image carrier in a counter direction of a rotation direction of the image carrier. To prevent the blade from causing vibration at an early stage, a setting powder can be put onto the surface of the image carrier and the cleaning blade to reduce the friction between them. For example, polyvinylidene fluoride resin can be used as such a setting powder.
Utilizing a setting powder as a lubricant does not provide a large lubrication effect if not enough setting powder is put on the surface of the image carrier or the cleaning blade. However, a cleaning defectiveness resulting from cohesion of lubricant may arise when too much setting powder is used.
In particular, when utilizing a contact-type charging member, such as a charging roller, for uniformly charging an image carrier with electricity, setting powder may fall off from the cleaning blade with a downstream side of movement of the image carrier relative to the cleaning blade when there is too much setting powder put on the image carrier. As a result, the setting powder may adhere to the charging member and an image defect may occur. On this account, as for a desired quantity of application of the setting powder, a small amount is desirable if possible. However, if only a small amount of setting powder is used there is a concern that the cleaning blade will become wound up, especially in an early stage. Therefore, to prevent the cleaning blade from being wound and chipped, and to prevent an image defect from occurring as a result of a sliding friction between the cleaning blade and the image carrier from an inadequate application of the setting powder, a technology is known in which an image pattern is formed and is used to determine supplying toner as a lubricant. In this operation the toner is conveyed where the cleaning blade comes in contact with the photosensitive drum, and the toner, acting as a lubricant, is supplied to a contact portion of the cleaning blade and the image carrier forcibly. In this technology, the toner is supplied to the contact portion surely. This technology is disclosed, for example, in Japanese Laid-Open Patent Application No. 1-108592, Japanese Laid-Open Patent Application No. 6-194917, and Japanese Laid-Open Utility Model Application No. 60-118172.
However, as for this technology, the application toner, as a lubricant, supplied on the image carrier may increase or accumulate with years of use. Therefore, a drawback of toner scattering may arise. As a result of researching this drawback by the present inventors, a relationship of abrasion between the image carrier and the cleaning blade was found.
An ability of a surface of the image carrier is good in a state of use at an early stage of an image forming apparatus, and thus a coefficient of friction between the image carrier and the cleaning blade is significantly changed by the presence or the amount of supply of lubricant. Accordingly, the cleaning blade can be easily wound up by an opportunity of the few.
On the other hand, as the surface of the image carrier and the surface of the cleaning blade are polished by toner or by each other, the cleaning blade becomes comfortable with the image carrier, and the coefficient of friction between the cleaning blade and image carrier decreases with aged deterioration. Accordingly, the cleaning blade is hard to become rolled up. For this reason, it becomes necessary to supply only a small quantity lubricant, such as toner, to the contact portion of the image carrier and cleaning blade over time.
A thickness of a surface layer of the image carrier (photosensitive layer) decreases with wearing, and a sensitivity of the image carrier also deteriorates. Accordingly, when a toner image pattern for toner concentration control is formed on the image carrier, and toner supplying to a developer is controlled based on a quantity of toner adhesion to the toner image pattern, even if the toner concentration in the developer is at a fixed density, the developing density of the toner image pattern falls, and the toner is replenished in a surplus amount in the developer by the fall of sensitivity of the image carrier, and toner scattering may then easily occur.
Furthermore, because of age deterioration of toner charging ability due to deterioration of a developing agent, toner scattering may increase. In this way, over time too much lubricant, such as toner, may be supplied to a contact portion between the image carrier and the cleaning blade in order to prevent the cleaning blade from being wound up, and even further, a problem may arise that the toner excess becomes scattered at both ends in a long distance direction of the cleaning blade, and then the toner may stick to the image carrier.
Recently, a contact-type transcription member, such as a transcription belt or transcription roller, has been adopted for the propose of ozone reduction. When toner scattering occurs in an image forming apparatus utilizing a contact type transcription member, because the scattering toner is transferred directly to the transfer, member there is the concern that detrimental effects such as filming of the transfer member or pollution in the image forming apparatus may occur.